Manufacture of nitric acid esters



G. E.`HINDS -MANUFACIURIl 0F NITRVIC ACID EST-'ERS Filed Oct. 30, 1959 July 22, 1941.A

INVENTOR.

GeorgeEH 'mds BY CAM ATTORNEY Patented July 22, 1941 MANUFAC'IRE OF NITRIC ACID ESTERS George E. Hinds, Philadelphia, Pa., assignor to Sliarples Chemicals Inc., a corporation of Dela- Application October 30, 1939, Serial No. 301,871

7 Claims.

The present invention pertains to the manufacture of secondary alkyl nitrates, and particularly to the manufacture of alkyl nitrates containing over three carbon atoms.

The esteriiication of aliphatic alcohols containing three or more carbon atoms has always presented particular ydiiilculties, largely due to the occurrence of side reactions which are diiicult to control. In the case of the manufacture of esters by treatment of secondary alcohols with nitric acid, these diiculties have been even more pronounced than in the nitration of primary alcohols, with the consequence that the yields provided by processes heretofore available have been very small.

The object of the present invention has been to afford a process which would have important economic advantages over processes heretofore available for the manufacture of compounds of -this character. In the development of a process for accomplishing this object, particular conslderation has been given to the following goals:

1. To utilize a cheaper source of raw material `than the secondary alcohols, in the esterication operation.

2. To minimize undesired side reactions, and

3. To produce a crude esterication mixture which could be more easily purified than mixtures available from prior art esterification processes.

The first of these goals is accomplished in accordance with the present invention by providing a process in which an olefin may be substiftuted for the alcohol in the esterification reaction, thereby making it possible to use olens derived from petroleum, or from other economical sources, :as the basis -o-f the secondary alkyl radical.

One of the most serious defects in prior art processes of manufacturing nitric acid esters has been the tendency of the alcohol subjected to esterication to become oxidized to produce the corresponding aldehyde or ketone and products of further oxidation of these compounds. This tendency is reduced in the practice of the present invention, by utilizing the olen as the source of the alkyl radical. The only danger of ketone formation in the practice of the process of the present invention is involved in the possibility that a small amount of secondary alcohol, formed as a. by-product by hydration of the oleiin. may be oxidized. Since there is very little of such alcohol present at any stage of the applicants process, the formation of ketones is almost co1n ple-tely avoided.

In a co-pending application of John F. Olin et al., Serial No. 240,514, filed November l5, 1938, for Purification of crude esteriiication mixtures, the difficulties involved in separation of la relatively pure ester from the esterni-cation mixture produced when aliphatic alcohols are esteriiied by nitric acid are discussed. These difficulties are solved, in the practice of the invention of that application, by a succession of washing steps with water and a base, followed by distillation of the washed mixture. The nitric .acid and most of the alcohol are eliminated by the washing steps, and the ester is separated from water and residual alcohol in the distillation steps.

There is very little alcohol in the crude reaction mixture of the present invention, and the separation 4of the reaction mixture into its constituents can therefore be accomplished with much more facility and efliciency than can the reaction mixture of the above-identified copending application.

'Ihe invention may be practiced in the manufacture of alkyl nitrates with primary olefins (i. e., straight chain olefins, or branched chain olefins in which the branch does not occur at a carbon atom connected to the double bond), regardless of the carbon content of the particular olen treated, but it is recommended particularly in connection with treatment of oleiins containing between three and nine carbon atoms.

Further objects and advantages of the invention, and the manner in which they have been attained, will be evident from a reading of the following detailed description in the light of the attached flow sheet, in which The single figure is a diagrammatic illustration of the practice of the invention.

In describing the invention in detail, we shall assume that the olen to be reacted with nitric acid is pentene-Z. This method of description is adopted solely for the purpose of convenience, as the invention is applicable to reaction of various primary olens containing from two carbon atoms to over nine carbon a-toms.

In :the practice of the invention, nitric acid is rst passed from container I0 to reactor I3. The reactor I3 is equipped with a heating jacket or coil, or with other suitable means for heating the reaction mixture to the best reaction temperature. The nitric acid passed from -container I0 to reactor I3 may vary in concentration between 20% and 100%, but nitric acid of between 35 and 65% strength is preferably employed. The strength of nitric acid used in the particular case will depend somewhat upon the reaction temperature and pressure. Thus, if the reaction is accomplished at atmospheric pressure and a temperature of approximately 40 C., :the best results are attained by the' use of nitric acid of approximately 65% concentration. If, on the other hand, the reaction is conducted at a temperature of 100 C., and about T5 pounds per square inch gauge pressure, acid of approximately 50% concentration is preferred.

After suflicient nitric acid has been passed to the reactor I3 to bring the level of acid in that reactor nearly up to the point from which material is withdrawn from that reactor through valve I5, the reactor is heated to the desired reaction temperature, and pentene-2 (or other primary olefin) is then pumped into the reactor from container II. At the same time, a small quantity of 50% urea solution may be pumped into the reactor I3 from container `I 2, in order to cause decomposition of any nitrous acid which may be produced during the course of the reaction.

The mixture in reactor I3 is preferably agitated continuously in order to keep the ingredients thoroughly mixed.

The pentene-Z reacts with the nitric acid in the container I3in accordance with the following equation:

H Nitric Pentenc2 acid Secondary amyl nltrate The reaction mixture passes continuously through the conduit controlled by valve I5, into decanter I4. IThe pressure in reactor I3 is controlled by control of the valve I5, and is maintained sufliciently high to keep the pentene-2 in the liquid phase. f

'Ihe mixture collected in the decanter I4 separates into two layers. The heavier layer is dilute nitric acid and a part of this nitric acid is continuously returned through the Valve I6 to the reactor I3. As the continuous operation proceeds, it will be desirable either to increase the strength of nitric acid continuously introduced into reactor I3, in order to compensate for dilution of the acid recycled through decanter I4 to the reactor, or to withdraw a part of the nitric acid from the system through valve I'I. Nitric acid Withdrawn through the valve 'I may be combined with nitric acid derived from other steps of the process, and this nitric acid may be re-concentrated and returned to the container I to be used in continued practice of the process. It will be understood that, in the continuous practice of the process, as illustrated in the flow sheet, nitric acid and pentene-2 will be continuously passed to the reactor I3 at approximately'the same rate that they are used up in the reaction and withdrawn through valve I5 to decanter I4. Urea solution from tank I2 may also be added to reactor |3 as needed.

The upper layer separated by decanter I4 consists of a solution of unreacted pentene-2, secondary amyl nitrate, and a very small amount of secondary alcohol, formed as a result of hydration of the pentene-Z. This upper layer is passed through a heat exchanger I8, where it is cooled, and is then passed to a mixer I9, in which the constituents of this upper layer are thoroughly mixed with water from container 25. This Washing operation, as Well as the Washing and decanting operations performed in the mixers I9, 2| and 2'| and decanters I4, 20 and 22, is performed under slight superatmospheric pressure, in order to minimize losses of pentene-Z by evaporation.

The mixture from mixer I9 is next passed to decanter 20. The wash Water separates as the heavier phase, and may be combined with dilute nitric acid discharged through valve I'I. This combination of aqueous liquids, each containing nitric acid, may be concentrated together, for reuse in the process, or for other appropriate use.

The upper (oil) layer from decanter 20 is next passed to mixer 2| Where it is thoroughly mixed with an alkaline solution capable of neutralizing the last traces of nitric acid, and effecting further washing of the mixture, (e. g., a 5% soda ash solution). The mixture from mixer 2| is next passed to a decanter 22, in which separation into aqueous and oil phases again occurs. The aqueous phase, containing the alkaline solution, may be returned through valve 23 to mixer 2|. It will be necessary, however, to remove alkaline solution periodically from the system through valve 24, and replace it with fresh solution from container 26, in order to maintain the desired strength of alkaline solution.

The oil layer from decanter 22 is next passed to a mixer 21, where it is mixed with a further quantity of water from container 25. The resulting mixture is passed to a decanter 28, which operates similarly to decanters I4, 2i) and 22, to separate the aqueous wash liquid from the oil phase, which contains the desired secondary amyl nitrate, pentene-Z, some water, and a Very small trace of secondary amyl alcohol.

The washed oil phase, removed as the upper layer from decanter 28, is passed through a heat exchanger 29, where it is heated to a temperature of approximately C. The mixture from heater 29 is passed to a fractionating column 30, which maybe operated under a pressure of about 20 pounds per square inch. Pentene-2 and a small amount of water are taken 01T overhead from this column at a temperature of about 60 C. This overhead mixture is condensed in condenser 3|. A part of the condensed mixture is refluxed, and the remainder is passed to a decanter 33, in order to effect separation of the pentene2, as the upper layer in the decanter, from the water, which forms the lower layer. The pentene-2 separated in this manner from the Water may be returned continuously to container I for re-use in the process.

The temperature in the steam-jacketed still pot 32 is maintained at about 110 C. during the practice of the process. The crude esteriiication mixture, consisting principally of secondary amyl nitrate, but containing a small quantity of secondary amyl alcohol and Water, is continuously drawn oil? from the still pot 32 to container 34. This esteriication mixture may be further puriiied by distillation, if desired.

It will be understood, of course, that Wide variations in the above conditions are possible. and that statements as to preferred temperatures, pressures, etc., refer particularly to conditions which are recommended for manufacture of seconda-ry amyl and closely related valkyl nitrates, suc'h as the butyl and hexyl nitrates.

Various modications will be obvious to those skilled in the art, and I do not therefore Wish to be limited except by the scope of the sub-joined claims.

As an example of one such modification, it is pointed out that the invention may be practiced by batch operation, instead of by continuous operation as discussed above. The olefin may be reacted with the nitric acid in a batch esterification vessel, for example, and the esterication mixture may then be subjected to the sequence of washing, neutralizing and distilling steps discussed above, or to other steps for purification of the crude ester.

The invention is applicable to the manufacture of cyclo-alkyl nitrates by reaction of cyclo-olenns, such as cyclo-hexene, with nitric acid, as well as to the reaction by which open chain alkyl nitrates are produced.

I claim:

1. The process of manufacturing a secondary alkyl nitrate which comprises heating a mixture of an olefin containing at least three carbon atoms chosen from the class consisting of straight chain olefins and branched chain olens in which the branch does not occur at a carbon atom connected to the double bond with nitric acid of between 20 and 100% concentration until the olen reacts with the nitric lacid to form the desired alkyl nitrate.

2. The process of manufacturing a secondary alkyl nitrate which comprises heating a mixture of an olen containing lbetween 3 and 9 carbon atoms and chosen from the class consisting of straight chain olefns and branched chain olens in which the branch does not occur at a carbon atom connected to the double bond with nitric acid of between 20 and 100% concentration until the olefin reacts with the nitric acid to form the desired alkyl nitrate.

3. The process of manufacturing a secondary alkyl nitrate which comprises heating a mixture of an olefin containing between 4 and 6 carbo-n atoms and chosen from the class consisting of straight chain oleflns and branched chain oleflns in which the branch does not occur at a carbon atom connected to the double bond with nitric acid of between 20 and 100% concentration until the olen reacts with the nitric acid to form the desired alkyl nitrate.

4. The process of manufacturing a secondary alkyl nitrate which comprises heating a mixture of an amylene chosen from the class consisting of straight chain amylenes and branched chain amylenes in which the branch does not occur at a carbon atom connected to the double bond with nitric acid of between 20 and 106% concentration until the amylene reacts with the nitric acid to form the desired alkyl nitrate.

5. The process of manufacturing a secondary alkyl nitrate Which comprises heating a mixture of an olen containing at least three carbon atoms chosen from the class consisting of straight chain olefins and branched chain olens in which the branch does not occur at a carbon atom connected to the double bond with nitric acid of between 35 and 65% concentration until the olefin reacts with the nitric acid to form the desired alkyl nitrate.

6. The process of manufacturing a secondary alkyl nitrate which comprises heating a mixture of an olein containing 'at least three carbon atoms chosen from the class consisting of straight chain olefins and branched chain o-lens in which the branch does not occur at a carbon atom connected to the double bond with nitric acid of between 20 and 100% concentration to a temperature above 40 C. until the olefin reacts with the nitric acid to form they desired alkyl nitrate.

7. The process of manufacturing a secondary alkyl nitrate which comprises heating a mixture of an olen containing 'at least three carbon atoms chosen from the class consisting of straight chain olefins and branched chain olens in which the branch does not occur at a carbon atom connected tothe double bond with nitric acid of between `20 and 100% concentration to a temperature above 40 C. under super-atmospheric pressure until the olefin reacts with the nitric acid to form the desired alkyl nitrate.

GEORGE E. HINDS. 

